1. Field of the Invention
The present invention relates to a method and machine for recovering heavy materials, such as gold, from placer ore.
2. Description of the Prior Art
Many different devices have been constructed for the purpose of extracting heavy materials, such as gold and other heavy metals and minerals from placer ore. One very significant problem with conventional gold recovery devices that are used to recover gold from placer ore is that the apparatus employed is unable to separate and recover very fine gold particles from gold bearing ore. As a consequence, much of the gold processed through conventional gold recovery systems is not separated from the ore, but is discarded along with the tailings. More specifically, conventional placer ore gold recovery devices will not recover gold having a particulate size finer than 300 mesh. That is, gold particles that will pass through a mesh screen having more than three hundred openings per inch are totally lost. Furthermore, conventional gold recovery systems discard most of the fine particles of gold having a mesh size in the range of 200 to 300. Naturally, this reduces the efficiency and profitability of conventional placer ore gold recovery operations considerably.
One disadvantage of conventional placer ore gold recovery systems is that as each new load of gravel ore is added to the system, a surge is created in the water flowing through the system. This surging effect carries away many of the fine particles of gold that are originally retained in the system.
A further disadvantage of conventional gold recovery systems involves the very large requirement for water that is necessary for their operation. In conventional gold recovery systems eighteen hundred gallons of water per minute are typically required to process one hundred cubic yards of ore per hour to achieve only marginally acceptable efficiency of separation of gold from the ore. Such vast quantities of water are sometimes unavailable at the sites at which gold bearing placer ore is found.
Furthermore, even where such quantities of water are available, the use of such vast volumes of water in placer recovery operations invariably produces a major environmental impact in the area. Also, as a result of the large volume of water required for operation of conventional placer ore recovery devices and their relatively low efficiency of gold recovery, large holding ponds are necessary to receive tailings, so that the fine particles which merely pass through conventional systems can settle after processing. Failure to provide such holding ponds for conventional gold recovery systems leads to a discharge of fine ore particulates in water, thus significantly adversely affecting the environment and wild life in areas where gold is typically mined.
The efficiency of gold recovery with conventional systems drops rapidly from an initial efficiency of recovery of about 90% during the first three hours of operation to a recovery rate of approximately 60%. Even this reduced efficiency of recovery can be maintained for only about four or five days. Thereafter, the efficiency of recovery drops even further to the point where continued profitability of operation is unacceptable without a complete shutdown of operations and cleaning of the equipment.
A further disadvantage of conventional placer ore gold recovery systems is the extensive time of cleanup that is required. Such systems normally require approximately three hours for cleanup, during which no gold is being recovered. This extensive cleanup time adds significantly to the cost of operations.
Other very significant disadvantages of conventional gold recovery equipment are the great bulkiness, large cost and difficulty in transporting the equipment required For example, several different models of gold recovery plants are manufactured by IHC Holland, a company headquartered in The Netherlands. A typical system of such a conventional IHC device requires three railroad cars or three trucks to transport the component parts of the plant to a ]ob site. Furthermore, the cost of such a plant that will process one hundred cubic yards of ore per hour is in excess of one-half of one million dollars. Moreover, due to the heavy weight and great bulk, such conventional equipment can only be transported to sites having good roads or railway access.